1. Field of the Invention
The present invention relates to a surrounding structure of a loudspeaker wherein the range of the elastic deformation of the surrounding structure of the loudspeaker, which is a support system for the diaphragm, is widened.
2. Discussion of the Related Art
FIG. 1 is a cross sectional view showing the generic structure of a conventional loudspeaker. The loudspeaker is formed to include a vibrating diaphragm 1, surrounding structure 2, damper 3, voice coil bobbin 4, magnet 5, center pole 6, plate 7, voice coil 8 and frame 10. A magnetic path for magnetic flux formed of the magnet 5, the center pole 6, the plate 7 and a magnetic gap 9 is referred to as a magnetic circuit M.
A specific radius direction of the vibrating diaphragm 1 is located along the X axis and the center axis is located along the Z axis. The surrounding structure 2 of the loudspeaker is an elastic member of an annular structure as seen in the +Z axis direction. The surrounding structure 2 of the loudspeaker has an attaching part 2a, attaching part 2b and curved part 2c. The surrounding structure 2 is secured to the peripheral part of the vibrating diaphragm 1 by means of the attaching part 2a provided along the inner periphery of the surrounding structure 2. The surrounding structure 2 is secured to the peripheral part of the frame 10 by means of the attaching part 2b provided along the outer periphery of the surrounding structure 2. The form of the cross section of the curved part 2c is, in many cases, curved to have a generic hollow and semi-circular form in the cross section of the surrounding structure 2 along a plane including the X axis and the Z axis.
The magnetic flux generated by the magnetic circuit M crosses the voice coil 8 at a portion of the magnetic gap 9. Electromagnetic force occurs when a driving current corresponding to an audio signal is applied to the voice coil 8 in accordance with Fleming's rule so that the vibrating diaphragm 1 vibrates associated with the voice coil bobbin 4 in the Z axis direction. Thus, sound is emitted from the vibrating diaphragm 1 including a dome.
The effective vibration diameter of a diaphragm of the loudspeaker is denoted as A1 as shown in the figure, which is equal to the distance between the right and left center positions of the curved part 2c located 180° opposite to each other. Accordingly, the center of the curved part 2c of the surrounding structure 2 is positioned A1/2 away from the center of the vibrating diaphragm 1. In general, the effective area of the vibrating diaphragm contributing to the sound pressure characteristics of a loudspeaker is determined by the effective vibration diameter A1.
The damper 3 and surrounding structure 2 constitute a support system for elastically holding the vibrating diaphragm 1 in the Z direction and in the radius direction with a predetermined positioning precision and, at the same time, for regulating the amplitude of the vibration in the upward and downward directions of the vibrating diaphragm 1 and voice coil bobbin 4. The outer periphery of the surrounding structure 2 is secured to the frame 10 using the attaching part 2b. The maximum amplitude and the linearity of the amplitude of the vibration in the upward and downward directions of the vibrating diaphragm 1 are determined by the elasticity characteristics and viscosity characteristics (damping characteristics), which are the characteristics of the damper 3 and surrounding structure 2.
The efficiency of a loudspeaker becomes higher as the effective vibration diameter A1 becomes greater. It is necessary to make the width (hereinafter, referred to as cross sectional width) of the curved part 2c of the surrounding structure 2 narrower in the radius direction for expansion of the diameter of the vibrating diaphragm while maintaining the same outer diameter of the loudspeaker in order to increase the efficiency of the loudspeaker.
The radius of curvature of the curved part of the surrounding structure 2 of the loudspeaker, wherein the cross section of the curved part is in a semi-circular form, can be reduced in order to narrow the width of the surrounding structure 2. According to this method, change in shape of the surrounding structure 2 following the vibration in the upward and downward directions of the vibrating diaphragm 1 and voice coil bobbin 4 becomes difficult. In this case, the maximum amplitude of the surrounding structure 2 and vibrating diaphragm 1 becomes smaller and the linearity of amplitude of the elastic deformation of the surrounding structure 2 reduces significantly. At the same time, the stiffness of the surrounding structure 2 increases and, therefore, the maximum sound pressure of the loudspeaker is prevented from increasing, and the lowest resonant frequency of the loudspeaker becomes higher. Therefore, reproduction of the low frequency range of sound becomes difficult and the sound quality deteriorates.